1. Field of the Invention
The present invention relates to a data communication system applied to a data communication terminal such as a paging receiver, and a data communication terminal using the system.
2. Description of the Related Art
In a paging system based on the POCSAG scheme, a common address data is stored in the ID-ROMs of a plurality of paging receivers so that a caller can perform simultaneous paging to a plurality of subscribers who are carrying paging receivers having the common address data by transmitting this address data from a telephone terminal through a switching center. This simultaneous paging method is called a group call method among those skilled in the art and is used as a paging service.
If, therefore, a caller transmits a question message requesting an answer, as message data, following the common address data by the group call method using a computer terminal connected to a telephone line, a plurality of subscribers who are carrying paging receivers which have simultaneously received this question message can prepare answers to the received question message, and can return the answers to the computer terminal which has sent the question message.
In transmitting a question message by using the group call and obtaining a plurality of answers in this manner, it is difficult for the user of the computer terminal, which has sent the question message, to specify a paging receiver (subscriber) in the group every time an answer is obtained. In addition, when a plurality of question messages are transmitted to the same group, it is difficult to discriminate a specific question message to which a given answer corresponds.
The exchange of a question message and answers in a group by the group call method in such a system is effective for only very limited purposes. That is, this method is not very convenient.
As a new paging service which replaces the conventional POCSAG scheme, a paging service based on an advanced radio paging system called RCRSTD-43 will be put into practice in Japan.
This paging system will be briefly described with reference to FIGS. 1A to 1C.
FIG. 1 shows a scheme of signal transmission which is employed in the above advanced radio paging system. The format (A) in FIG. 1 shows a data configuration. The format (B) in FIG. 1 shows a cycle configuration. The format (C) in FIG. 1 shows a frame configuration.
The data configuration (A) in FIG. 1 consists of 15 cycles which are numbered "#0" to "#14". The 15 cycles are transmitted at one-hour intervals. The cycle configuration (B) in FIG. 1 consists of 128 frames which are numbered "#0" to "#127". The 128 frames are transmitted at four-minute intervals. The frame configuration (C) in FIG. 1 consists of eight pieces of information, i.e., a first synchronous portion S1, frame information FI, a second synchronous portion S2, block information BI, an address field AF, a vector field VF, a message field MF, and an idle block IB.
In this frame configuration, the eight pieces of information define the following contents.
More specifically, the first synchronous portion S1 defines the frame type (the modulation scheme and transmission rate) of this frame. The frame information FI defines the frame number of the frame, a cycle number at which the frame is present, and the like. The second synchronous portion S2 defines timing information which is used to establish a reception timing in a called paging receiver in transmitting data in accordance with the frame type defined by the first synchronous portion S1. The block information BI defines word numbers at which the address field AF and the vector field VF respectively start, and the necessary numbers of words. The address field AF defines ID data, specifically address data, stored in each called receiver. The vector field VF is defined in a one-to-one correspondence with the address field AF. The vector field VF defines a word number at which the message field MF is started, the necessary number of words, a vector type (tone only, a numerical message, and the like) specifying a message to be transmitted. The message field MF is used to store message data to be actually transmitted. The idle block IB is an unused block, in which a pattern of "1"s or "0"s is set.
According to paging services using the above advanced radio paging system, therefore, various services which cannot be provided by the conventional POCSAG scheme can be realized.
As one of the services, a service based on a group call method using temporary address data can be realized, in addition to a service based on the conventional group call method using group address data.
In this method, a plurality of paging receivers which do not share group address data are simultaneously paged. The method will be described below.
1. A caller designates the group call mode using temporary address data and transmits the call numbers of a plurality of paging receivers to be called and a common message to a center (paging control center).
2. When the group call mode is designated by the caller using the temporary address data, the center transmits address field AF contents address data for calling the designated paging receivers thereto, together with vector field VF contents vector data of a simplified instruction vector type which defines the temporary address data and a frame number at which the temporary address data is stored.
3. Upon terminating this vector data, each of the called paging receivers writes the temporary address data in an address register in a decoder, and also writes the frame number data at which the temporary address data is stored in a frame register, thereby controlling the reception frame timing. At the designated frame number, each paging receiver detects the temporary address data in accordance with the address field AF.
4. When each paging receiver detects the temporary address data at the designated frame number in accordance with the address field AF, the receiver receives the common message stored in the successive message field MF, notifies that the message is terminated, and displays it.
According to the above method, therefore, a plurality of paging receivers to be subjected to simultaneous paging need not have common address data. That is, a more convenient group call method can be realized.
In the above method, however, the following problem is posed.
When a caller designates the group call mode using temporary address data, he/she must input all the call numbers of a plurality of paging receivers to be called through a telephone terminal connected to the center. If the caller is to use a push-phone through a public telephone network, a cumbersome input operation is required. The caller is therefore liable to make a mistake.
The present invention has been made in consideration of the above problem, and has as its object to provide a data communication system in which a caller can selectively perform batch transmission of a question message to a plurality of callees and totalize a plurality of answers to this question in a readable form, and a data communication terminal using the system.